Polypivalolactone fibers and a method for their manufacture

ABSTRACT

A DRAWN, TENACIOUS POLYPICALOACTONE FIBER HAVING A DENSITY OF 1.17 AT THE MOST AND A SUFFICIENT HEAT-SETTING ABILITY WHICH COMPRISES A POLYMER CONSISTING ESSENTIALLY OF POLYPIVALOLOACTONE WHICH CAN BE OBTAINED BY UNIFORMLY INCORPORATING A POLYMER CONSISTING ESSENTIALLY OF POLYPIVALOLACTONE WITH A SMALL AMOUNT OF AT LEAST ONE ORGANIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF TRICRESYLPHOSPHATE, TRIXYLENYL PHOSPHATE, TRINONYLPHENYL PHOSPHITE AND TRIOCTADECYL PHOSPHIRE, EXTRUDING THE MIXTURE THROUGH AN ORIFICE OF A SPINNERET, APPLYING HIGH DRAFT TO THE EXTRUDED MIXTUTE WHILE IT IS STILL IN A MOLTEN OR PLASTICIZED STATE TO THEREBY FORM UNDRAWN FIBERS, AND THEREAFTER, DRAWING SAID UNDRAWN FIBER. SAID UNIFORM ADMIXTURE OF SAID COMPOUND LEADS TO BROADENED RANGES OF THE CONDITIONS SUITABLE FOR SPINNING, IMPROVED FEASIBILITY OF OPERATION, RETARDATION OF CRYSTILLIZING VELOCITY OF THE POLYMER AFTER BEING SPUN AND SOLIDIFIED, AND MARKEDLY IMPROVED ORIENTATION.

United States Patent U.S. Cl. 260-306 R 3 Claims ABSTRACT OF THE DISCLOSURE A drawn, tenacious polypivalolactone fiber having a density of 1.17 at the most and a sufficient heat-setting ability which comprises a polymer consisting essentially of polypivalolactone which can be obtained by uniformly incorporating a polymer consisting essentially of polypivalolactone with a small amount of at least one organic compound selected from the group consisting of tricresyl phosphate, trixylenyl phosphate, trinonylphenyl phosphite and trioctadecyl phosphite, extruding the mixture through an orifice of a spinneret, applying high draft to the extruded mixture While it is still in a molten or plasticized state to thereby form undrawn fibers, and thereafter, drawing said undrawn fiber. Said uniform admixture of said compound leads to broadened ranges of the conditions suitable for spinning, improved feasibility of operation, retardation of crystallizing velocity of the polymer after being spun and solidified, and markedly improved orientation.

CROSS REFERENCE TO A RELATED APPLICATION This application is a division of our co-pending application, Ser. No. 656,350, filed July 27, 1967, now Pat. No. 3,575,907.

BACKGROUND OF THE INVENTION (a) Field of the invention The present invention relates to a method for manufacturing highly oriented and tenacious fibers which comprise a polymer consisting essentially of polypivalolactone (which will hereinafter be referred to merely as polypivalolactone fibers) by melt spinning highly crystalline polypivalolactone and subsequently drawing the spun undrawn fibers.

The preferred utility of the polypivalolactone fibers manufactured, according to the method of the present invention, as filaments or staple fibers covers a wide range from garments to industrial purposes, such as woven fabrics, knitted goods, carpets, nonwoven cloths, felt, web cloth material for synthetic leathers, paddings, papers, filtering cloths and tire cords.

(b) Description of the prior art In order to make a useful fiber by melt spinning a fiberforming thermoplastic organic synthetic linear polymer, such as a polyamide and a polyester, it has been generally accepted as being necessary to include a step of drawing the fiber after the latter is spun. Specifically, it is known that the so-called undrawn fibers after being spun have an extremely low degree of orientation of the molecular chains in the polymer. Especially those undrawn fibers consisting of a polymer, such as a polyester, also have an extremely low degree of crystallinity and are poor in mechanical strength required of such fibers. Their orientation and crystallinity can be improved by subjecting them to drawing and it is only after the undrawn fibers are drawn that the fibers can acquire the mechanical strength desired of such fibers. It is also known that in order to facilitate the orientation by drawing of fibers consisting of a highly crystalline polymer in the stage after the melt-spinning step, it has been the practice to lead the fibers into a quenching liquid medium immediately after they are spun and before drawing, while the fibers are still in a molten or plasticized state, to rapidly cool and solidify the polymer by such quenching and to thereby minimize their degree of crystallinity and also to produce an amorphous molecular arrangement.

In view of the characteristics of polypivalolactone polymer, that it crystallizes rapidly and easily to a very high degree, it is impossible to expect sufficient orientation of the molecules in the polypivalolactone fibers nor it it possible to expect to obtain fibers having a superior physical property, from the application of the aforesaid melt-spinning or drawing conditions of the prior art. This is endorsed by the statement made in the specification of the French Pat. No. 1,231,163 and the paper of R. Thiebaut et al. (Industrie des Plastiques Modernes, Mar. 13, 1962), both of which point out that there is a tremendous difliculty in manufacturing fibers from polypivalolactone on an industrial basis because of the inconveniences that, owing to the unusually high crystallinity of polypivalolactone, the amorphous molecular arrangement cannot be acquired from the mere quenching of this polymer at the time of the formation of a film. This polymer attains a maximum degree of crystallinity during a very short period of time, resulting in an opaque film. Also, during the step of producing a fiber, this polymer crystallizes rapidly immediately after the melt-spinning, making the orientation by subsequent drawing extremely diflicult so that the resulting fibers are brittle and lack desirable mechanical properties. Because of the fact that the production of fibers from polypivalolactone is accompanied by these great ditficulties, there have been made very few studies on the techniques of manufacturing fibers from this polymer, except for the statements dealing with a few manufacturing conditions which are made in the specifications of U.S. Pat. No. 2,658,055, British Pat. No. 766,347 and Japanese patent publication No. 9810/1966. Specifically, U.S. Pat. No. 2,658,055 contains a statement reading to the effect that polypivalolactone develops an orientability when it has a molecular weight corresponding to an intrinsic viscosity (1 of 0.5 or more, and polypivalolactone having such a molecular weight can be subjected to melt spinning. In Example 4 of the specification of said U.S. patent, it is described that by extruding polypivalolactone at a temperature just below the melting point, namely, in the range of from 230 degrees centigrade to 235 degrees centigrade and under a high pressure of 4,000 pounds per square inch and by thereafter manually drawing the extruded fiber to a length four times the original length, a drawn fiber showing an X-ray orientation angle of 17 degrees was obtained. In Example 5 thereof, there is described the acquisition of a fiber having a high degree of crystallinity, such as a density of 1.20 (24.5 degrees Centigrade), by a method similar to the above from polypivalolactone having an intrinsic viscosity of 0.90.

British Pat. No. 766,347 discloses in Example 7 the fact that, by melt spinning polypivalolactone at a temperature above its melting point, namely, at 285 degrees centigrade, and by drawing the fiber to a length four times the original length at degrees centigrade, a fiber having such properties as are represented by a tensile strength of 1.9 gr./d. and an elongation of 19.9 percent was obtained.

However, the method of said US. patent requires an extremely high pressure at the time of spinning and, therefore, it is difficult to apply this method industrially since there are involved various problems with respect to the feasibility of the operation, the property of the produced fiber and the designing of the manufacturing apparatus, and also from the viewpoint of the maintenance of the apparatus. Especially, the high density (1.20) of the fiber obtained according to this prior method means that the degree of crystallinity of the polymer constituting the fiber is close to the maximum value which this polymer can attain, and that the heat-setting ability of the fiber is already lost. Accordingly, this shows, for example, the fact that it is impossible to manufacture a crimped fiber of an excellent quality.

Also, with the property of the fiber obtained from the application of the method of said British patent, one could not expect a superior position of this fiber in industry over other fibers. Furthermore, the Japanese Patent Publication No. 9810/1966 carries a mere general statement that such fibers are given the necessary orientation by the application of a large draft effect during melt spinning and then the degree of orientation of such fibers may be augmented by conducting drawing immediately after the fibers are melt spun. However, this publication lacks a clear cognizance of the optimum spinning conditions.

SUMMARY OF THE INVENTION After an extensive and detailed research on the physical property and the fine structure of polypivalolactone, the inventors have discovered that while this polymer belongs to the family of polyesters, as will be seen from its chemical structure, it is an extremely unique polymer which is completely different, in both its physical character and fine structure, from other fiber-forming polyesters which are represented by, for example, polyethylene terephthalate and similar polyesters. After further detailed and systematic study on the spinnability of polypivalolactone, it has been found that the spinning method and the spinning condition for ordinary polyester fibers can never be applied to polypivalolactone. Rather, the same requires new, specific spinning conditions and that by the application of a spinning method incorporating the new, specific spinning conditions, it becomes possible to manufacture a highly oriented, tenacious, transparent fiber having a sufiicient heat-setting ability and a desirable elastic recovering ability which can never be obtained by the prior spinning methods, and, based on such knowledge, the inventors have discovered an improved method.

As a result of the subsequent continuous detailed research on the relationship between the rheological property and the spinnability of polypivalolactone at the time of melting, the inventors have found that, while the rheological property of the melted polypivalolactone depends a great deal on the temperature and the pressure employed at the time of melting as compared with other polymers used in ordinary melt spinning, this high degree of dependency of the rheological property of polypivalolactone on the temperature and the pressure can be substantially minimized and stabilized by incorporating, with polypivalolactone, at least one organic compound selected from the group consisting of tricresyl phosphate, trixylenyl phosphate trinonylphenyl phosphite and trioctadecyl phosphite. Also, this minimized and stabilized dependency of the rheological property of polypivalolactone on the temperature and the pressure at the time of melting is orientation effected at the time of spinning under draft and during the subsequent drawing step.

It is, therefore, an object of the present invention to provide a polypivalolactone fiber which is highly oriented and which has sufiicient heat-setting ability and which is tenacious, transparent, uniform in quality and greatly useful.

Another important object of the present invention is to provide an improved industrial method for quite easily manufacturing such a useful fiber by spinning and drawing a polypivalolactone fiber without the need for any special mechanical equipment.

Still another object of the present invention is to provide an industrial manufacturing method in which desirable manufacturing conditions for obtaining such fiber are specified.

Yet another object of the present invention is to provide a crimped fiber consisting essentially of polypivalolactone and having a markedly superior extension percentage of crimp and recovery percentage of crimp.

Other objects of the present invention will become apparent by reading the following description.

While the present invention concerns the techniques of melt spinning and drawing a polymer consisting essentially of polypivalolactone, it is to be understood that said polymer is such that it is incorporated uniformly, prior to being subjected to melt extrusion, with a small amount of an additive which consists of at least one organic compound selected from the group consisting of tricresyl phosphate, trixylenyl phosphate, trinonylphenyl phosphite and trioctadecyl phosphite.

The term polymer consisting essentially of polypivalolactone used in the present invention means polypivalolactone or a copolymer or blend polymer of polypivalolactone as the principal component with other polymer or polymers.

The term polypivalolactone which is used in the present invention means a linear condensation polymer consisting essentially of recurring ester structural units expressed by the formula:

This polymer is readily manufactured by the method of polymerization of hydroxypivalic acid or its ester as is described in US. Pat. No. 2,658,055 or by the employment of the method of polymerizing pivalolactone as is described in the specification of British Pat. No. 766,347. The term a copolymer of polypivalolactone means a copolymer which is prepared by copolymerizing the aforesaid polypivalolactone with up to 25 mol. percent of other lactones, such as fl-propiolactone, a,u-diethylpropiolactone. A blend polymer of polypivalolactone as the principal component and of other polymer or polymers is a composition consisting of polypivalolactone or a copolymer of polypivalolactone as the principal component which is blended with other polymer or polymers in an amount essentially not affecting the property of said principal component. It is needless to say that polypivalolactone containing ordinary additives, such as a dye, a pigment and a stabilizer, is also usable.

It is necessary that the polypivalolactone which is applicable to the present invention have an intrinsic viscosity ranging between 0.7 and 5.5, and preferably in the range between 0.8 and 4.0. Polypivalolactone having less than 0.7 is markedly low in fiber-forming ability, and unless it is given an extremely high spinning draft at the time of spinning, the fiber cannot be endowed with utility, nor can it exhibit such excellent properties as are obtained by the present invention. A very high value of intrinsic viscosity, on the other hand, will result in a restriction of the fiber manufacturing conditions. Specifically, in case (1 has a value exceeding 5.5, there will occur an extreme lowering of the fluidity of the polymer in its molten state and this will give rise to a difiiculty in the spinning operation. In general, however, there is an advantage that the degree of orientation of an undrawn spun fiber can be increased by the application of a smaller amount of spinning draft as increases in value, provided that the efliciency of the spinning operation is not taken into account, and as a result, it becomes easy to produce a tough fiber.

The intrinsic viscosity is determined by the use of a mixed solvent consisting of six parts of phenol'and four parts of orthochloro-phenol and by the employment of a temperature of 30 degrees centigrade and it is calculated from the following equation:

0'0 Sp/c wherein:

c represents the concentration expressed in grams of polypivalolactone contained in 100 ml. of solution formed by dissolving polypivalolactone in the aforesaid solvent;

' is defined by (1 -1 in which 17 represents the viscosity of the aforesaid solution, and no represents the viscosity of said solvent.

Esters of phosphoric acid and phosphorous acid can be used effectively as an additive in the present invention. They include, for example, tricresyl phosphate, trixylenyl phosphate, trinonylphenyl phosphite and trioctadecyl phosphite. These additives can be used either independently or in the form of a mixture of two or more of them.

The suitable range of the amount of the foregoing additives to be used is between 0.1 and 10.0 percent by weight, and preferably, between 1.0 and 6.0 percent by weight of the total weight of the composition comprising a polymer consisting essentially of polypivalolactone and the additives. Those additives having a low molecular weight display a sufficient effect by being used in a small amount. In the event that the amount added is less than 0.1 percent by weight, however, it does not bring about a substantial efiect on the improvement in the drawability of the spun fiber in the steps subsequent to the first step, as compared with the instance where no additive is used. In the event that the amount is in excess of 10.0 percent by weight, on the other hand, the result will be a reduced spinnability which will be accompanied by a reduction in the uniformity of the size of the final fiber.

The aforesaid additives are incorporated, either independently or as a mixture of two or more of them, with polypivalolactone after the completion of polymerization of polypivalolactone and are mixed thoroughly therewith while being stirred so that the additive may be dispersed uniformly.Polypivalolactone containing such additive in the state of a uniform dispersion is transferred to the first step, namely, the melt-spinning step either directly or after being shaped into granules or chips. Satisfactory results can be obtained also by transferring granules or chips of polypivalolactone not containing the aforesaid additive uniformly dispersed therein but having such an additive adhering thereto or mixed therewith to the first step. When required, such polypivalolactone may be melted to effect a thorough mingling of the additive in the polypivalolactone and then made into chips before being transferred to the spinning step. In any case, it is important that the aforesaid additive which has been incorporated with polypivalolactone be present therein in such a state that the additive is uniformly dispersed or mingled in the polypivalolactone by a mechanical operation, such as mixing by stirring, While in the melted state. This mixing by stirring may be carried out by means of a screw housed in an apparatus such as a melt extruder or by means of a pump or like means.

The aforesaid additive, which is thus added and dispersed in polypivalolactone, retains its state of being molten, mingled and dispersed in the molten polypivalolactone for an extended period of time. The additive contained in the aforesaid form in polypivalolactone displays the following named various excellent effects in association with the subsequent steps, without separating from the mixed state undernormal melt-spinning conditions and without affecting in any way the desirable chemical as well as physical properties of polypivalolactone:

(a) It minimizes as well as stabilizes the great de pendency of the melting and rheological property of polypivalolactone on the temperature and pressure employed;

(b) It contributes to the attainment of the broadening of the range of the intrinsic 'viscosity of polymers suitable for spinning and also to the enhancement of the feasibility of operation;

(c) -It improves the spinnability of the molten polymer and detachability of the molten polymer from the nozzle;

(d) It retards the rapid crystallization of the polymer in the stage after the spun fiber is solidified;

(e) It extremely improves the orientation in the steps of spinning and drawing.

As has been described above, the polypivalolactone which has been mixed uniformly with an additive can be spun and drawn easily by the use of a known melt-spinning and take-up apparatus and drawing apparatus, without requiring any special mechanical equipment.

'INCORPORATION BY REFERENCE Pursuant to the Commissioners Notice dated I an. 15, 1969 (34 Fed. Reg. 883), there is incorporated by reference (1) column 7, line 39 through column 24, line 15 and (2) column 24, line through column 25, line 13, of US. Pat. No. 3,575,907.

Example 1 To polypivalolactone having an intrinsic viscosity (1 of 3.35 was added three percent by weight of tricresyl phosphate, and in a manner similar to that employed in Example 11 of Pat. No. 3,575,907, the mixture was made into chips. Using a screw extruder and under the conditions, i.e., by the use of a spinneret having one orifice of 0.5 mm. in diameter, at a spinning temperature of 280 degrees centigrade, at an extrusion rate of 5.7 gr./min., at a take-up speed of 710 mt/min. and at a spinning deformation ratio of 30, the chips were spun into an atmosphere held at 20 degrees centigrade and a relative humidity of percent, with the result that an undrawn fiber having R =0.89 and a size of 72 d. and having a residual elongation of 492 percent was obtained. This undrawn fiber was then drawn at a room temperature to 5.1 times the original length, and thus, a tenacious and excellently uniform filament having a fiber size of 14.9 d., fiber size fluctuation of 6.2 percent, a tensile strength of 8.4 gr./d., an elongation of 26 percent, a Youngs modulus of 680 kg./mm. a knot strength of 8.1 gr./d. and a loop strength of 15.9 gr./d., was obtained.

Example 2 To polypivalolactone having an intrinsic viscosity (1;) of 1.6 was added 2.5 percent by weight of trioctadecyl phosphite, and in the manner described in Example 11, of Pat. No. 3,575,907, chips were produced. From the Equation 1, the spinning deformation ratio required for the melt spinning of said chips was 63 or more. Using a heat grid-type melt-spinning apparatus, and under the conditions, i.e., by the use of a spinneret having 18 orifices each having a diameter of 0.4 mm., at a spinning temperature of 275 degrees centigrade, at a take-up speed of 500 m./ min. and at an extrusion rate of 12.3 gr./min., the chips were melt spun into an atmosphere held at 20 degrees centigrade and arelative humidity of percent. As a result, undrawn fibers having'R:=0.88, and a size of 249 d./18 fil., were obtained. Continuously thereafter, the undrawn fibers were drawn at room temperature to 3.7 times the original length, and thus, tenacious filaments having a size of 70 d./ 18 fil., a tensile strength of 6.1 gr./d., an elongation of 35 percent, a Youngs modulus of 520 kg/mm? and a shrinkage in boiling water of 3.0 percent were obtained.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A drawn, tenacious polypivalolactone fiber having a maximum density of 1.17 and a heat-setting ability, which is formed of a composition comprising a polymer consisting essentially of polypivalolactone having an intrinsic viscosity in the range of from 0.7 to 5.5 and from 0.1 to 10.0 percent by weight of at least one organic compound selected from the group consisting of tricresyl phosphate, trixylenyl phosphate, trinonylphenyl phosphite and trioctadecyl phosphite, said organic compound being uniformly distributed in said polymer.

2. A fiber according to claim 1, wherein the amount 8 of said organic compound contained in the polymer is from 1.0 to 6.0 percent by Weight of the total weight of the composition.

3. A fiber according to claim 1, in which the polypivalolactone has an intrinsic viscosity in the range of from 0.8 to 4.0.

References Cited UNITED STATES PATENTS 1/1967 Knobloch et a1. 26078.3 R X 1/1969 Armour et a1. 26078.3 R X 

